1. Field of the Invention
This invention relates to butterfly or disc-type valves of the type having a body with a flow passageway and a disc with a circumferential sealing surface, the invention providing means of indicating the integrity of the seal when the valve is in closed position.
2. Description of the Prior Art
Butterfly valves have long been utilized in industry and are commonly employed because of their economy of construction, simplicity, durability, ease of repair, and many other reasons. In many applications of valves it is desirable to be able to determine, when the valve is in the closed position, that no leakage is occuring through the valve. This is sometimes referred to as "integrity assurance". One means of obtaining integrity assurance is to place two valves in position in series with a short pipe or conduit therebetween. When the valves are both closed, an opening in the connecting conduit will indicate whether one valve or the other is leaking. This arrangement, while functioning satisfactory, is extremely expensive and consumes much space. In addition, it requires the simultaneous operation of two valves which is cumbersome and is also subject to human error.
In order to provide means of checking the integrity of valves, particularly valves of the butterfly type, others have provided means within the valve itself. Of particular relevance is U.S. Pat. No. 4,067,352 entitled "VALVE HAVING INTEGRITY ASSURANCE MEANS" issued Jan. 10, 1978. In this patent a butterfly valve is disclosed including a valve disc having parallel spaced apart circumferential sealing contacts. Formed in the body of the valve, and extending through the body sealing surface, is a small diameter opening. When the valve is in the closed position, the spaced apart sealing contacts are to either side of the opening and thus communication is provided through the valve body so that leakage past either one of the paralleled sealing contacts can be detected.
While the invention illustrated in U.S. Pat. No. 4,067,352 represents an improvement over the prior state of the art, nevertheless, it introduces some difficulties. Since the opening through the valve body must extend through the body sealing surface, such opening provides means for a possibility of leakage of fluid from within the valve to the space between the valve seat and the valve body. The arrangement of the patent requires the valve disc to be precisely positioned when in closed position so that the valley area between the adjacent disc sealing contacts is in alignment with the opening in the valve body. If the disc is not precisely positioned, then this communication is not established and the integrity of the valve cannot be verified. Another difficultly is that of maintaining a controlled diameter of an opening through an elastomeric member. For the valve to close against fluid pressures, it is necessary that a resilient force exists between the elastomeric seat and the disc and this, of course, tends to slightly displace the elastomeric member which, if the opening through the member is of small diameter, tends to close it.
For these and other reasons, the valve design as taught in U.S. Pat. No. 4,067,352, has not found commercial acceptance.
It is an object of the present invention to provide an improved butterfly valve having leak detecting means which overcomes the disadvantages of the prior art.
More particularly, an object of the present invention is to provide an improved butterfly valve having leak detecting integrity assurance means which does not require an opening extending through the valve body and, more importantly, does not require an opening extending through the valve seat.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims taken in conjunction with the attached drawings.